When a ControlNet Link Fails, Production Stops
A plant engineer once watched a single ControlNet cable fault take an entire process line down. The controller was healthy, the I/O was healthy, but the network path was gone. That is exactly the problem the Allen-Bradley 1756-CNBR/D was built to solve. This ControlNet redundant bridge module gives ControlLogix systems two independent ControlNet channels, so a link failure does not become a production failure.
What the 1756-CNBR/D Actually Does
The 1756-CNBR/D belongs to the Allen-Bradley ControlLogix / Bulletin 1756 platform, carrying the Series D suffix. It is a ControlNet redundant bridge module with 2 channels, bridging ControlNet A/B networks to the chassis backplane. In plain terms, it keeps communication alive between ControlLogix controllers and ControlNet devices when one network path drops.
Because the module mounts in a standard 1756 ControlLogix chassis, it follows the platform rule that any module can sit in any slot. The chassis backplane (ControlBus) then carries high-speed communication between modules, and the chassis itself is powered by a dedicated 1756 power supply module.
Lifecycle Status: Discontinued
Rockwell Automation lists the 1756-CNBR/D as discontinued, with a discontinuation date of 2024-12-31. The recommended replacement is the 1756-CN2R. If you still run ControlNet redundant architectures, verify current lifecycle status and availability with Oil AutoTech before ordering.
Key Specifications at a Glance
| Parameter | Value |
|---|---|
| Part Number | 1756-CNBR/D |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Series | ControlLogix / Bulletin 1756 |
| Product Type | ControlNet Redundant Bridge Module |
| Channels | 2 |
| Current Draw | 970 mA @ 5.1 V, 1.7 mA @ 24 V |
| Isolation | 30 V |
| Operating Temperature | 0 to 60 C |
| Storage Temperature | -40 to 85 C |
| Network Interface | ControlNet A/B to backplane |
| Configuration Software | Studio 5000 Logix Designer |
| Lifecycle Status | Discontinued (2024-12-31) |
| Replacement | 1756-CN2R |
Reading the Power and Isolation Numbers
The 970 mA draw at 5.1 V tells you this module leans on the chassis backplane supply, so power budgeting across the rack matters. The 30 V isolation figure separates the ControlNet side from the backplane side, which protects logic from network-side electrical noise. The 0 to 60 C operating range matches the wider ControlLogix family.
Where This Module Earns Its Keep
Redundant ControlNet architectures appear most often where a dropped link costs real money. In oil and gas processing, redundant bridges keep controllers talking to remote I/O across long cable runs. In power generation and water treatment, the same logic applies: two paths, one job. The 1756-CNBR/D fits those cases because it bridges ControlNet A/B directly to the backplane rather than adding another conversion layer.
For buyers replacing a failed unit, the practical question is simple. Do you need the exact discontinued part, or do you migrate to the 1756-CN2R? Oil AutoTech helps with that selection call, and we keep fast-dispatch spares ready for oil, gas and industrial automation lines.
Installation and Setup Notes
Mount the module in a 1756 ControlLogix chassis and confirm the chassis power supply can cover the total load. Configure the module in Studio 5000 Logix Designer, the same environment used for the rest of the ControlLogix family. Because this is a redundant bridge, plan the A and B cable routes as physically separate paths — otherwise redundancy buys you very little. Follow the manufacturer’s installation documentation for all wiring details.
Maintenance and Long-Term Reliability
ControlNet faults usually trace back to cabling, connectors, or termination rather than the bridge itself. Inspect network cabling and connections periodically, watch chassis temperature, and keep the module seated firmly in its slot. If a link drops repeatedly, check the physical layer first. Given the discontinued status, treat any working 1756-CNBR/D as a spare you want on the shelf, not one you want to order in a crisis.
Compatibility and Integration
The module works within the ControlLogix / Bulletin 1756 platform and is configured through Studio 5000 Logix Designer. It bridges ControlNet A/B networks to the chassis backplane. ControlLogix chassis-based communication modules in this family support EtherNet/IP, ControlNet, DeviceNet, and DH+/Remote I/O, so the 1756-CNBR/D slots into mixed ControlNet environments. Confirm your exact cabling and network layout with your supplier before installation.
Before You Order
Check three things: your chassis power budget, whether your architecture still requires ControlNet redundancy, and whether the 1756-CN2R replacement fits your migration plan. If you need the original discontinued module, contact Oil AutoTech today for pricing and availability.
Frequently Asked Questions
Is the 1756-CNBR/D still in production?
No. Rockwell Automation lists it as discontinued as of 2024-12-31, with the 1756-CN2R named as the replacement.
How many ControlNet channels does this module provide?
It provides 2 channels, bridging ControlNet A/B networks to the ControlLogix chassis backplane.
What software configures the 1756-CNBR/D?
You configure it in Studio 5000 Logix Designer, formerly RSLogix 5000, like other ControlLogix modules.
What are the power requirements?
The module draws 970 mA at 5.1 V and 1.7 mA at 24 V from the chassis supply.
Can I use the 1756-CN2R instead?
The 1756-CN2R is the listed replacement. Confirm compatibility with your exact application before swapping.
